This invention relates generally to valves for controlling the flow of hydraulic fluid from a source to a load and more specifically to a direct drive valve. More specifically the invention is directed to a direct drive valve which is controlled by motor control signals generated by a digital signal processor.
Direct drive valves include a drive mechanism which moves a spool which in turn controls the flow of fluid from a source to a load. The drive mechanism is limited in its travel whether the-drive motor is a limited angle rotary motor or a linear drive motor such as a solenoid or a voice coil. In such devices it is desirable that the output flow from the direct drive valve follows certain predetermined parameters. For example, it is often desired that the flow from the valve be linear in response to the command signals applied to the valve. It however may under certain circumstances be required that the flow follows other predetermined patterns. In order to accomplish the desired flow, the prior art generally shapes the ports through which the fluid flow passes to provide the desired output flow pattern. In some instances the output flow is controlled by attempting to linearize portions of the flow path and then amplifying the command signal to accomplish a more linearized flow. See for example the structure as disclosed in U.S. Pat. No. 5,285,715 which is assigned to the assignee of this application. An additional method for obtaining the desired output from a direct drive valve is shown in U.S. Pat. No. 5,551,481 which is also assigned to the Assignee of the present application. As is therein shown, the fully packaged drive motor is positioned upon a hydraulic stage and an appropriate control signal, which is indicative of a desired and predetermined output is applied to the drive motor. The output of the hydraulic stage is measured. The drive motor is then positioned with respect to the hydraulic stage by rotating and moving the drive motor, so as to obtain the desired output from the hydraulic stage. Prior art U.S. Pat. No. 4,513,782 discloses a traditional electrohydraulic servovalve as opposed to a direct drive valve in which a matching circuit is disposed between the input command signal and the servovalve control coil to assist in linearizing the output response of the electrohydraulic servovalve. This is accomplished by generating a look-up table which is stored in the memory and is used to modify the input command signal to cause the hydraulic magnitude output to be as desired at each available address. Such prior art processes and structures work adequately for the purpose intended. However these devices require a substantial amount of additional labor and may require substantial manual adjustment of each of the direct drive valves at the time of manufacture. As a result, the cost and time for manufacture is high.
It is therefore desirable to provide a direct drive valve which may be compensated through the utilization of a digital controller to provide the desired predetermined flow merely by manipulation of the control signal to the direct drive valve.
A direct drive valve includes a spool for controlling the flow of fluid from a source thereof to a load, a means for driving the spool and a digital signal processor for providing motor control signals to the means for driving the spool.
A system for providing compensation to command signals for a direct drive valve so that the fluid flow output therefrom conforms to a desired predetermined flow includes means for generating raw flow data from an uncompensated valve, means for calculating compensation variables analogous to a difference between the raw flow data and the desired predetermined flow from the valve, and means for applying the compensation variables to a digital signal processor for generating motor control signals for application to the direct drive valve to produce the desired predetermined flow therefrom.
A method for providing a predetermined fluid flow output from a direct drive valve includes generating raw flow data for the direct drive valve, comparing the raw flow data to a desired predetermined flow, calculating compensation variables analogous to the differences between the flow data and the predetermined flow, providing a digital signal processor to control the direct drive valve and loading the compensation variables into the digital signal processor.